1. Field of the Invention
This invention relates to an adsorbent suitable for selectively adsorbing mercury from mercury-containing aqueous or gaseous materials.
2. Prior Art
The source of mercury and its compounds to be removed by adsorption or other methods is found largely in waste liquid or gas discarded for example from the sites of manufacture or use of chemicals, electrolytes, pharmaceuticals, insecticides, bactericides, agricultural drugs, dry cells, fluorescent lamps, instruments, or from the incinerators for city garbage, industrial wastes and sewage, or from mines, metal refineries, research institutes, hospitals and so on.
Generally, heavy metals can be disposed of by coagulative precipitation in the well known manner. This method however is not effective for the treatment of mercury which must be held to a very stringent control rate of 0.005 milligram per liter under existing legal environmental regulations.
Chelate resins are effectively used to adsorb and reduce mercury ions in a waste fluid to the statutory limits, but these resins are extremely costly and economically not feasible where they must be used in large amounts to handle high concentrations of mercury. Because of this and in view of the fact that mercury exists in complex forms in different wastes and its behaviour is not clearly known, there may be considered a pre-treatment in which a cascade of coagulative precipitation steps is used, or combinations of sulfurization, active carbon treatment and other methods. However, these alternatives would entail considerable initial investments and complicated control systems to maintain optimum operating conditions throughout the various stages of the process.